btrfs: clean the old superblocks before freeing the device

btrfs_rm_device frees the block device but then re-opens it using
the saved device name.  A race exists between the close and the
re-open that allows the block size to be changed.  The result
is getting stuck forever in the reclaim loop in __getblk_slow.

This patch moves the superblock cleanup before closing the block
device, which is also consistent with other callers.  We also don't
need a private copy of dev_name as the whole routine operates under
the uuid_mutex.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 11 insertions, 27 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c356ce332229..be2c8b35c3ae 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1846,7 +1846,6 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path, u64 devid)
         u64 num_devices;
         int ret = 0;
         bool clear_super = false;
-        char *dev_name = NULL;
 
         mutex_lock(&uuid_mutex);
 
@@ -1882,11 +1881,6 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path, u64 devid)
                 list_del_init(&device->dev_alloc_list);
                 device->fs_devices->rw_devices--;
                 unlock_chunks(root);
-                dev_name = kstrdup(device->name->str, GFP_KERNEL);
-                if (!dev_name) {
-                        ret = -ENOMEM;
-                        goto error_undo;
-                }
                 clear_super = true;
         }
 
@@ -1936,14 +1930,21 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path, u64 devid)
                 btrfs_sysfs_rm_device_link(root->fs_info->fs_devices, device);
         }
 
-        btrfs_close_bdev(device);
-
-        call_rcu(&device->rcu, free_device);
-
         num_devices = btrfs_super_num_devices(root->fs_info->super_copy) - 1;
         btrfs_set_super_num_devices(root->fs_info->super_copy, num_devices);
         mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
 
+        /*
+         * at this point, the device is zero sized and detached from
+         * the devices list.  All that's left is to zero out the old
+         * supers and free the device.
+         */
+        if (device->writeable)
+                btrfs_scratch_superblocks(device->bdev, device->name->str);
+
+        btrfs_close_bdev(device);
+        call_rcu(&device->rcu, free_device);
+
         if (cur_devices->open_devices == 0) {
                 struct btrfs_fs_devices *fs_devices;
                 fs_devices = root->fs_info->fs_devices;
@@ -1962,24 +1963,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path, u64 devid)
         root->fs_info->num_tolerated_disk_barrier_failures =
                 btrfs_calc_num_tolerated_disk_barrier_failures(root->fs_info);
 
-        /*
-         * at this point, the device is zero sized.  We want to
-         * remove it from the devices list and zero out the old super
-         */
-        if (clear_super) {
-                struct block_device *bdev;
-
-                bdev = blkdev_get_by_path(dev_name, FMODE_READ | FMODE_EXCL,
-                                                root->fs_info->bdev_holder);
-                if (!IS_ERR(bdev)) {
-                        btrfs_scratch_superblocks(bdev, dev_name);
-                        blkdev_put(bdev, FMODE_READ | FMODE_EXCL);
-                }
-        }
-
 out:
-        kfree(dev_name);
-
         mutex_unlock(&uuid_mutex);
         return ret;